The present invention relates to a microelectromechanical (MEMS) spectrophotometer and, more particularly, to a MEMS cylindrical reflective diffraction grating spectrophotometer.
Spectrophotometers are optical instruments which separate optical signals according to their wavelengths. They have broad applications including color identification in flat panel displays or electronic cameras, color control for xerographic printing, optical spectroscopy for chemical analysis, environmental monitoring, and process controls which are related to color identification. To date, commercial spectrophotometers tend to be of rather large size because they are formed by assembling bulky optical elements, mechanical parts, detectors, and microelectronic chips into a system. The present day assembly process needs high precision and is labor intensive, keeping the cost of conventional bench top spectrophotometers from being affordable.
Many additional applications of interest arise if spectrophotometers were significantly lower cost, lighter weight, smaller size, rugged, and incorporated signal processing capability in the instrument. In xerographic printing, a spectrophotometer is a key component in a closed-loop color control system which will enable the printers to generate reproducible color images in a networked environment. The development of a compact, low cost spectrophotometer is thus important in realizing high performance printing systems.
With the advance of micromachining technology, it is now possible to build various microstructures, movable mechanical components, micro optical elements, including free-space, out-of-plane lenses and gratings, sensors, and electronic circuits on silicon chips using modified IC processes that are able to produce thousands of these devices in batch on silicon wafers. Over the past decade, much effort has been devoted to the development of micro spectrophotometers using MEMS technology.
A microelectromechanical spectrophotometer having a Fabry-Perot cavity filter is taught in U.S. Pat. No. 6,295,130, commonly assigned with the present application and herein incorporated by reference. The Fabry-Perot cavity thickness is tuned electrostatically to resolve the spectral distribution of the transmitted light signal to make a color sensing system.
A MEMS spectrophotometer with a stationary concave grating formed in a monolithic substrate is disclosed in U.S. Pat. No. 6,249,346, commonly assigned with the present application and herein incorporated by reference. The stationary grating focuses light on a movable photodiode array
It is an object of this invention to provide a MEMS spectrophotometer with a rotating cylindrical reflective diffraction grating on a Rowland circle.